The present invention is related to optical devices for fiberoptic systems and networks and, in particular, to erbium-doped fiber amplifiers and their components.
In modern fiberoptic transmission systems and networks, such as Dense Wavelength Division Multiplexing (DWDM) optical networks, the erbium-doped fiber amplifier (EDFA) is employed nearly universally to amplify optical signals. The EDFA provides for optical-to-optical conversion and avoids OEO (Optical-Electrical-Optical) conversion where received optical signals were converted into electrical signals, retimed, reshaped and regenerated back into optical signals. EDFAs have the advantages of wideband, i.e., the ability to amplify signals over a wide range in frequency, high signal gain, low noise figure, high output power and low polarization sensitivity.
Hence the EDFA provides for savings in cost and complexity. Nonetheless, EDFAs today are still expensive and are used primarily in the so-called “long-haul” or “backbone” fiberoptic networks which link nodes over long, intra-continental and even inter-continental, distances. Most of these fibers have been laid and the present challenge to fiberoptic developers are the “metro-,” i.e., citywide, or smaller, networks. Much development effort has been directed toward a compact (for ease of installation) and cost-effective optical amplifier for metro-networks and upgrades of optical nodes in the long-haul networks. This effort includes conventional wideband EDFAs, semiconductor optical amplifiers (SOAs) and erbium-doped waveguide amplifiers (EDWAs). However, wideband EDFA is quite expensive for some applications, such as metro-networks and power compensation. In this case, narrow band EDFA is much more cost effective than wideband counterparts. SOAs have disadvantages of high noise figures, polarization-dependent gain (PDG) and cross talk; their applications are very limited. Likewise, EDWAs require very high pump power to provide sufficient gain and output power, while their noise figures are quite high. Therefore, EDFAs are still the most efficient approach in power conversion efficiency.
The present invention provides for a novel, low-cost, and highly compact EDFA.